Showing a reason why Storm changed her hair would be better because the kind of hairstyle that Storm had in x-men 2 and 3 are definitely not Storm's hairstyles.

If you have a 2 hour long ensemble film with many characters, they are simply not going to waste time focusing on why Storm changes her hairstyle from hilm to film. There are waaaaaayyyy more important aspects of Storm that need to be fleshed out first (like, an origin story perhaps) before they focus on something cosmetic like that.

Remember, Jean Grey and Rogue had non-classic hairstyles too. It's called adapting a comic to film--and in these situations, the filmmakers made a concious effort to modernize everyone's look versus translating the comic book looks so literally. This is why they were wearing black leather uniforms, why Logan's "Wolverine" hair wasn't so extreme in certain films and why young Xavier still has yet to go bald.

They are marketing these films to appeal to the general audience, not just the fanboys. I don't like what they've done to Storm's hair in these films either, mind you, but I seriously doubt Bryan Singer, Louise Mingenbach and others sat down and wrote out some traumatic scene explaining why Storm cuts her hair shorter with each film...I just don't think anyone is thinking that deeply about it. LOL